This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to a Japanese Patent Application 2001-382878, filed on Dec. 17, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a control apparatus for controlling a shift operation in a vehicle automatic transmission assembled to a torque converter with a lock-up clutch and capable of automatically switching a shift stage. The shift operation is actually controlled by engaging/disengaging plural friction engagement elements assembled in the automatic transmission. More particularly, this invention pertains to a control apparatus capable of reducing torque fluctuation of an output shaft assembled in an automatic transmission, which may occur along with a clutch-to-clutch shift operation, wherein a good shift feeling can be attained.
According to a conventional automatic transmission, torque transmitted to an off-going friction engagement element which is adapted to be disengaged along with shift operation in the automatic transmission is required to be reduced corresponding to increase of torque transmitted to an on-coming friction engagement element which is adapted to be engaged along with the shift operation. A one-way clutch has been employed for reducing the torque transmitted to the off-going friction engagement element. However, somewhat recent developments have led to an automatic transmission in which a clutch-to-clutch shift operation is performed by controlling hydraulic pressure of oil supplied to the friction engagement element as a substitute for the one-way clutch.
According to the above-described clutch-to-clutch shift operation, torque of an output shaft of the automatic transmission suddenly may fluctuate and a shift feeling may become worse unless the hydraulic pressure control can be executed properly. More specifically, assuming that a timing to reduce the torque transmitted to the off-going friction engagement element is delayed relative to a timing to increase the torque transmitted to the on-coming friction engagement element, a so-called interlocked condition may be established in the transmission so that the torque of the output shaft may be rapidly decreased. On the other hand, assuming that the timing to reduce the torque transmitted to the off-going friction engagement element is too premature relative to the timing to increase the torque transmitted to the on-coming friction engagement element, a rotation speed (hereinafter, referred to as RPM) of an input shaft of the transmission, i.e. a rotation speed of a turbine wheel may be increased. Therefore, the torque of the output shaft may be rapidly reduced.
In order to solve the aforementioned problem, this type of automatic transmission has been considered to perform a so-called slip amount control, whereby the increase of the torque transmitted to the on-coming friction engagement element is controlled to wait for the time to be started while generating a slip by reducing the torque transmitted to the off-going friction engagement element. The slip amount control can be executed by a controller (i.e. a feedback controller) which can perform a proportional-plus-integral control for controlling the torque transmitted to the off-going friction engagement element for matching the slip amount with a target slip amount. Therefore, the torque fluctuation of the output shaft due to fluctuation of the slip amount may be able to be effectively restrained.
However, according to a vehicle disposing a torque converter with a lock-up clutch between a vehicle driving power source such as an engine and the automatic transmission, load applied to the driving power source from the automatic transmission, i.e. an inertia of the input shaft of the transmission widely varies in accordance with an engagement condition of the lock-up clutch. For example, when gain of the controller and phase characteristics thereof are adapted for preventing the output shaft torque from fluctuating along with the clutch-to-clutch shift operation during the lock-up clutch being engaged, the gain of the controller may become excessive along with the clutch-to-clutch shift operation during the lock-up clutch being disengaged. The output torque may be unnecessarily generated with large pulsation. Therefore, the shift feeling may become worse.
Accordingly, the present invention therefore seeks to provide an improved control apparatus for controlling the shift operation in the automatic transmission, which can ensure a favorable shift feeling along with the clutch-to-clutch shift operation independently of the engaged/disengaged condition of the lock-up clutch.
According to an aspect of the present invention, a control apparatus for controlling a shift operation in an automatic transmission performing a predetermined shift stage by maintaining respective plural friction engagement elements to be engaged or disengaged includes a fluid type transmitting mechanism (21) for transmitting an output from a vehicle driving power source to the automatic transmission, a lock-up clutch (22) disposed in parallel to the fluid type transmitting mechanism and adapted to be engaged or not to be engaged and adapted for transmitting the output from the driving power source to the automatic transmission during the lock-up clutch at least being engaged, a lock-up clutch controlling means (50) for controlling the lock-up clutch to be engaged or not to be engaged in accordance with a vehicle driving condition, and a clutch-to-clutch shift operation controlling means (50) for generating a slip by reducing torque transmitted via an off-going friction engagement element and performing a shift operation by increasing torque transmitted via an on-coming friction engagement element. The off-going friction engagement element of the plural friction engagement elements is switched from the engaged condition to the disengaged condition along with the shift operation from a shift stage to the other shift stage. The on-coming friction engagement element of the plural friction engagement elements is switched from the disengaged condition to the engaged condition along with the shift operation from the shift stage to the other shift stage;
The clutch-to-clutch shift operation controlling means includes an input shaft rotation speed obtaining means (step 1520) for obtaining a value corresponding to a rotation speed of an input shaft of the automatic transmission, an output shaft rotation speed obtaining means (step 1510) for obtaining a value corresponding to a rotation speed of an output shaft of the automatic transmission, and a slip amount controlling means (step 1650 and 1700) having a feedback controller for controlling the torque transmitted via the off-going friction engagement element for matching a control slip amount obtained based upon the values corresponding to the input shaft rotation speed and the output shaft rotation speed with a predetermined target slip amount and switching a gain of the feedback controller and phase characteristics thereof in response to the engagement condition of the lock-up clutch.
The value corresponding to the input shaft rotation speed includes the input shaft rotation speed or a value obtained by applying a low-pass filtering process to the input shaft rotation speed. The low-pass filtering process removes a frequency of the input shaft rotation speed being substantially equal to or greater than a predetermined frequency for removing high frequency noise such as sensor noise included in the input shaft rotation speed. The value corresponding to the output shaft rotation speed includes the output shaft rotation speed or a value obtained by applying a low-pass filtering process to the output shaft rotation speed. The lo-pass filtering process removes a frequency of the output shaft rotation speed being substantially equal to or greater than a predetermined frequency for removing high frequency noise such as sensor noise included in the output shaft rotation speed. The low-pass filtering process removes fluctuation of the output shaft rotation speed due to the fluctuation of the intolerance of the driving circuit.
The feedback controller controls the torque transmitted via the off-going friction engagement element for matching the control slip amount obtained based upon the values corresponding to the input shaft rotation speed and the output shaft rotation speed with the target slip amount. In this case, the gain of the feedback controller and the phase characteristics thereof are switched corresponding to the engagement condition of the lock-up clutch. The slip amount can be hence effectively controlled by the feedback controller having preferable characteristics corresponding to inertia of an input shaft of the automatic transmission which is changed in response to the engagement condition of the lock-up clutch, wherein the slip amount won""t fluctuate. Therefore, the clutch-to-clutch shift operation can be performed with a good shift feeling with only slight fluctuation of an output shaft of the transmission.
According to another aspect of the present invention, the slip amount controlling means further includes a notch filtering means (1525) for obtaining a notch filtered input shaft rotation speed by applying a notch filtering process for removing frequency component in a predetermined frequency domain to the value corresponding to the input shaft rotation speed obtained by the input shaft rotation speed obtaining means. In this case, the slip amount controlling means substantially switches the gain of the feedback controller and the phase characteristics thereof by obtaining the control slip amount based upon the value corresponding to the input shaft rotation speed prior to be applied with the notch filtering process and the value corresponding to the output shaft rotation speed during the lock-up clutch being engaged and based upon the notch filtered input shaft rotation speed and the value corresponding to the output shaft rotation speed obtained by the output shaft rotation speed obtaining means while the lock-up clutch has not been engaged.
Therefore, the control slip amount won""t be fluctuant and the actual slip amount can be effectively controlled not to fluctuate, wherein a good shift feeling can be obtained upon the clutch-to-clutch shift operation. Further, the clutch-to-clutch shift operation can be properly performed while the lock-up clutch has not been engaged only by adapting the feedback controller for performing the clutch-to-clutch shift operation during the lock-up clutch being engaged. In other words, the feedback controller is not required to be additionally adapted for performing the clutch-to-clutch shift operation while the lock-up clutch has not been engaged. Therefore, load and energy can be effectively saved and manufacturing cost can be reduced.